1. Field of the Invention
This invention relates to furnaces and in particular to heat exchangers for use in furnaces.
2. Description of the Related Art
In one form of a conventional domestic furnace, air to be heated is passed in heat transfer association with a plurality of stacked serpentine heat exchanger elements forming a heat exchanger encased in a cabinet. Each heat exchanger element defines a flow path for hot products of combustion produced by combustion of fluid fuel, typically, such fuel may include, for example, oil or natural gas. The hot products of combustion, in passing through the heat exchanger elements, transfer their heat energy to the air to be heated, conventionally referred to as the room air, and are then exhausted through a suitable flue.
Prior art serpentine heat exchangers are typically manufactured from either a continuous tube or in two halves joined together, e.g., xe2x80x9cclam-shellxe2x80x9d, by known bending and/or joining techniques. To increase the heat transfer between the combustion products, contained within the heat exchanger, and the ambient environment residing at the exterior of the same, it is known that forcing the flow to become non-laminar, especially at the latter portion of the exchanger, greatly improves heat transfer.
Flow diverters and separators of many types were added to the interior structure of the exchangers to increase the flow turbulence, however such methods significantly increased manufacturing costs of the heat exchangers. To lessen the expense yet retain acceptable levels of exchanger performance both continuous tube and clamshell type heat exchanger elements included external deformations to create internal flow xe2x80x9cturbulatorsxe2x80x9d to increase heat transfer performance at an acceptable additional cost. However, the need has arisen to decrease the size of furnace cabinet and accompanying heat exchanger assembly therein while sustaining equal or increased heat transfer characteristics of the heat exchanger assembly.
U.S. Pat. No. 5,346,001 issued to Rieke et al. discloses a heat exchanger which employs a turbulator region comprised of multiple, interfacing and closely arranged deformations within the clamshells. The deformations are successively and contiguously arranged within each clamshell to promote turbulence, and consequently, enhanced heat transfer within this region. However, the turbulator region causes a significant decrease in flow velocity along portions of the interior walls of the turbulator region which corresponds to a decrease of heat transfer along these wall portions.
A clamshell type heat exchanger assembly which causes turbulent flow, however increases flow velocity at the site of passageway walls to increase heat transfer between the heat exchanger elements and room air would be desirable.
Further, a clamshell type heat exchanger utilizing conventional materials of construction which sealably contains flue gases while using less heat exchanger materials, consequently providing a significant cost decrease, as compared to prior art exchangers, would be desirable.
The present invention overcomes the disadvantages of prior art furnaces by employing a heat exchanger including a plurality of clamshell elements having trapezoidal enhancements to significantly increase the heat transfer and provide an overall smaller or compact furnace corresponding to a reduction of manufacturing and assembly costs.
The present invention provides a heat exchanger for use with a furnace including a plurality of heat exchanger elements having internal structures which receive hot products of combustion and transfer heat to room air being externally forced over each heat exchanger element. Each heat exchanger element includes a pair of clamshells, having depressions facing one another. The depressions are sealingly clamped to one another and form a passageway wall and a serpentine fluid passageway therebetween. The depressions within the clamshells define an inlet and an outlet in fluid communication through the serpentine flow passageway. A plurality of enhancements are disposed within the depressions defined in the clamshells and extend into the flow passageway. Each enhancement is provided with a corrugation and each corrugation includes a substantially trapezoidal cross-section. Longitudinally positioned passageway wall portions extend between adjacently positioned enhancements within each clamshell. The plurality of enhancements are structured and arranged with the passageway wall portions to direct a flow of products of combustion received in the heat exchanger element along the passageway wall at a non-zero velocity.
The present invention heat exchanger, in one form thereof, includes a heat exchanger element having enhancements in one clamshell coacting with enhancements in the other clamshell to increase the heat transfer between the flow of hot products of combustion through the element with room air flowing externally over the element. Each enhancement defines upstream and downstream ramping portions separated by a plateau and having respective angles of inclination and declination.
The heat exchanger of the present invention further provides at least one heat exchanger element having a pair of clamshells. The clamshells include a serpentine fluid passageway therein which receives hot products of combustion. The fluid passageway includes an inlet channel and at least one enhancement channel positioned downstream relative to the inlet channel. The inlet and enhancement channels are in fluid communication with one another and a plurality of enhancements are disposed within the enhancement channel. The enhancements reduce zones of recirculation formed by the hot products flowed through the passageway and correspondingly increase the heat transfer between the hot products of combustion and room air being urged externally over the heat exchanger element.